The present invention relates to a metal band saw backing material which is welded to the high speed steel used as an edge material.
Metal band saws are generally formed by welding high speed steel used as an edge material to inexpensive low alloy steel used as a backing material for the purpose of saving expensive high speed steel. After an edge material has been welded to a backing material, both materials are subjected to heat treatment which is suited to the high speed steel used as the edge material, i.e., quenching at about 1200.degree. C. to 1220.degree. C. and tempering at 540.degree. C. to 580.degree. C.
Although JIS G4051 S50C. (carbon steel) and AISI6150 are generally used as backing materials, these backing materials have the problem that, if they are subjected to heat treatment under conditions for quenching and tempering which are the same as those for high speed steel, the toughness of the backing materials is deteriorated owing to the excessively high quenching temperature, and the hardness is also deteriorated owing to the excessively high tempering temperature. Such heat treatment therefore provides backing materials with insufficient tensile strength and causes the deterioration in the fatigue strength of backing materials, this resulting in the occurrence of fracture therein.
In order to solve these problems, the applicants of the present invention investigated materials which allow sufficient hardness to be secured even under conditions for heat treatment which are the same as those for high speed steel. As a result, the applicant could develop new alloys and bring them into practical use, as disclosed in Japanese Patent Publication Nos. 54-5366, 55-32778 and 61-12022.
A description will now be give of the latest trend of metal band saws which is a clue to the present invention.
A metal band saw is endless-welded and driven by the two wheels, which are installed in a band sawing machine so as to cut a material to be cut which is mainly a steel material and is firmly and horizontal held between the wheels. The metal band saw is loaded with tension between the wheels so that no cutting curvature occurs in the steel material and is repeatedly subjected to bending stress along the wheels when being driven.
The wheels have an inclination relative to the horizontal direction so that the metal band saw is loaded with torsion corresponding to the inclination of the wheels. The metal band saw is therefore subjected to the loads of tensile stress and bending and torsion stress during when being driven.
In the above-described metal band saw, the following problems have recently arisen:
A first problem is that, since cutting conditions are gradually made severe with an increase in the number of kinds of hard-to-cut materials such as super heat resistant steel and stainless steel and an improvement in cutting efficiency, backing materials are also required to have high performance and a long life.
A second problem is that, since high tension is required for improving cutting precision and backing materials are used in a cutting apparatus under a high stress load which has never been applied, conventional body materials have short life of up to fracture, and there is a demand for a backing material having higher fatigue strength.